Fix description for digit keys.

The 'Used for miscellaneous..." description appears to be ripped
directly from MSDN docs, and is misleading BS. If there is a
keyboard where these codes are used for varying characters,
then it is just as likely that other codes will vary as well.
Comment cleanup - /Input/*.cs

* GamePadButtons.cs: Line lengths + capitalization fixes.
* GamePadDPad.cs: Line lengths and capitalization fixes.
* GamePadDeadZone.cs: Fixed line lengths, capitalization, and 360
  references.
* GamePadState.cs: Remove more 360 references that were possibly
  ripped from MSDN; These structs/methods are not specific to 360
  controllers.
* GamePadThumbSticks.cs: Line lengths / capitalization.
* GamePadTriggers.cs: More line lengths and capitalization fixes.
* GamePadType.cs: Self-documenting code should not hide one value in
  random place.
Merge pull request #210 from 3vi1/monogame-sdl2

Comment cleanup - /Input/*.cs